23.) Diabetes Insipidus

Question 1

What is Diabetes Insipidus (DI)?

Answer 1

A condition characterized by an imbalance in the body’s water regulation, where the kidneys are unable to concentrate urine.

Question 2

What are the forms of Diabetes Insipidus?

Answer 2

1. Central DI: caused by insufficient levels of circulating antidiuretic hormone (ADH).
2. Nephrogenic DI: characterized by defective renal ADH receptors.
3. Gestational DI: decreased ADH during pregnancy due to increased metabolism by aminopeptidase from the placenta.

Question 3

What are the causes of Central Diabetes Insipidus?

Answer 3

Idiopathic (50% of cases), trauma, hypothalamus processes (tumors, sarcoidosis, TB, meningitis).

Question 4

What are the causes of Nephrogenic Diabetes Insipidus?

Answer 4

Most common cause in adults is chronic lithium use; other causes include hypercalcemia, pyelonephritis, and demeclocycline.

Question 5

What is the pathogenesis of Diabetes Insipidus?

Answer 5

ADH enables the integration of aquaporins into the plasma membrane of collecting duct cells for reabsorption of free water. ↓ ADH or defective renal ADH receptors lead to impaired urine concentration and dilute urine.

Question 6

What are the urine osmolarity levels in Diabetes Insipidus?

Answer 6

Normal osmolarity: 500-800 mOsm/kg; Complete DI: below 300 mOsm/kg; Partial DI: 300-500 mOsm/kg.

Question 7

What are the clinical features of Diabetes Insipidus?

Answer 7

Polyuria (5-15 liters daily), nocturia, restless sleep, daytime sleepiness, and polydipsia (thirst).

Question 8

How is Diabetes Insipidus diagnosed?

Answer 8

Urine shows low osmolarity and low specific gravity. Plasma osmolarity varies: Normal (275-295 mOsm/kg), Primary polydipsia (255-280 mOsm/kg), DI (280-310 mOsm/kg).

Question 9

What is the dehydration test for Diabetes Insipidus?

Answer 9

No fluids are given, and urine osmolarity is measured every hour. If urine osmolality is <300 mOsm/kg with serum hyperosmolality, desmopressin is injected. An increase >50% indicates severe pituitary DI; a smaller or absent response indicates nephrogenic DI.

Question 10

What are the ADH levels in Central and Nephrogenic Diabetes Insipidus?

Answer 10

ADH levels are low in Central DI and normal or elevated in Nephrogenic DI.

Question 11

What is the treatment for Diabetes Insipidus?

Answer 11

Treat underlying condition and initiate a low sodium and low protein diet. Central DI: desmopressin orally (100-400 micrograms 2-3 times daily).

Nephrogenic DI: Thiazide diuretics (hydrochlorothiazide 25-50mg daily).